With their immense towing and hauling abilities, heavy-duty pickup trucks are trickier to evaluate than, say, a Porsche Boxster. Renting a racetrack or rocketing down our favorite back road is pretty straightforward, but we don’t always have a 40-foot horse trailer or a spare bulldozer to lug around, let alone the commercial driver’s license that such a load can require. Which is why we joined GMC in the Rocky Mountains for some jobsite schooling with the updated 2017 Sierra 2500HD and 3500HD—the tonier twins of the 2017 Chevrolet Silverado HD—trucks that round out Detroit’s latest class of junior Peterbilts.
We put Chevy’s latest HD trucks to work at last year’s State Fair of Texas during an all-too-brief orientation. But exercising these rigs on the open road, at high altitudes, and under various loads is a different matter. Our drive started out in Moab, Utah, and meandered over craggy, snow-capped peaks to Telluride, Colorado (8750 feet above sea level), with stops along the way to exercise General Motors’ new Duramax diesel engine and the Sierra’s enhanced workday skills.
Whereas Ford took a more comprehensive approach to revising its 2017 F-series Super Duty trucks—including stronger frames, fresh aluminum bodywork, and a boost up to 925 lb-ft of torque for its Power Stroke turbo-diesel V-8—GM focused primarily on a new diesel powertrain and the refinement of its big trucks at their working limits. A 360-hp 6.0-liter gasoline V-8 carries over as the base engine in the Sierra HD, but our time was spent exclusively with turbo-diesel models in the top-grade Denali trim, which accounts for about half of GMC’s heavy-duty sales, with most buyers choosing diesel power.
Distinguished by a prominent, ram-air-style hood scoop—which adds to the conventional fender-well intake to facilitate engine cooling—the diesel Sierra HD now pumps out 910 lb-ft of torque at 1600 rpm, putting it between the Ford and the 900-lb-ft Ram 3500 with the optional Aisin automatic (lesser 2500- and 3500-series Rams make 660 or 800 lb-ft, depending on gearbox). GM’s new Duramax 6.6-liter V-8, known internally as L5P, however, tops them all in horsepower, with 445 ponies to the Super Duty’s 440 and the Ram’s max of 385. The standard and diesel-only six-speed Allison automatic transmission (the gas engine is paired with a Hydra-Matic six-speed automatic) sports new electronic controls and has been fortified in key areas, as has the driveline leading to the carryover axles with 3.73:1 differential ratios. Altogether, the powertrain requires an upcharge of about $9000 on the Sierra HD, depending on the cab and bed configuration.
About 90 percent of the L5P has been updated versus the previous LML version, which produced 397 horsepower and 765 lb-ft of torque. The cast-iron block and basic valvetrain architecture carry over, but almost everything else is new, including the aluminum cylinder heads, the forged-steel crankshaft, the pistons, the variable-vane turbocharger, the high-pressure fuel-injection system, and the exhaust system with its accompanying selective catalytic reduction aftertreatment components. A new insulated oil pan has been fitted for noise reduction, which helps in making the big Sierra eerily quiet at speed; there continues to be some minor diesel clatter at idle and a powerful growl with the accelerator floored, but the cabin is luxury-car calm even with the engine straining under a heavy load. Despite the power bump, GM also claims a 35 percent reduction in tailpipe emissions for the L5P compared with the old Duramax.
The Sierra/Silverado HD is generally the lightest and wieldiest pickup in its class, and much of the sheetmetal, cabin, and underpinnings are the same as when the current trucks debuted for 2015. GM’s independent front suspension provides surprising steering feel and precision for a big rig—despite the wheel still being slightly offset to the right of the driver’s center—and the ride quality of 2500HD models when unladen is largely free of serious shakes and hopping over rough pavement. (The sturdier 3500HD versions are less forgiving yet still quite comfortable.) When saddled with only their own mass, which should total about four tons for the 3500HD, these behemoths also feel downright speedy for their size, although we’ll have to wait for an actual test truck to confirm that.
As with any heavy-duty pickup, additional weight in the bed or in tow calms things down significantly; 2500s can haul up to 3534 pounds and tow up to 18,100, with 3500s rated at up to 7153 and 23,300 pounds. While that towing capacity is considerably less than Ford’s 32,000-pound maximum, GMC reasons that a minuscule proportion of buyers actually tug that much, and GMC instead chose to refine the composure of its HDs when hitched to the 10,000- to 20,000-pound trailers that most drivers contend with. We barely noticed a flatbed trailer loaded with Polaris ATVs (about 5000 pounds) behind a crew-cab 2500HD 4×4, and even a 10,000-pound enclosed car hauler posed little challenge on the mountain grades of our drive route—which doesn’t surprise considering GMC’s claim that a 2017 3500HD Duramax towing its maximum load was 40 seconds quicker than before climbing up the SAE’s Davis Dam testing grade. Put your foot down and even a loaded-up GMC will move out with authority. As in the Super Duty, attaching the maximum weight to the Sierra HD’s bumper-mounted hitch (14,500 pounds for the 2500 and 20,000 for the 3500) does not require the use of an additional weight-distributing attachment. Maximum fifth-wheel trailer weights are 18,100 pounds for the 2500HD and 23,300 for the 3500HD.
While an additional five tons trailing behind definitely slows down the Sierra HD and taxes its braking system, there’s little sense of the trailer trying to drive the truck, which imparts a significant amount of confidence behind the wheel. GM also has further improved the already impressive grade-braking ability of its big rigs, with revised controls for the transmission’s tow/haul setting and greater exhaust braking, both of which can be used separately or together. Like a Sport mode in a performance car, activating tow/haul keeps the transmission in a lower gear (for increased engine braking) and brings aggressive up- and downshifts, although shifts remain relatively smooth considering the mammoth forces at play on the truck. Small accelerator modulations can set the revs on descents, and on all but the most extreme grades with the heaviest loads, you can limit speed without touching the brake pedal, keeping the stoppers cooler for when you really need them. Both features also tie into the Sierra’s cruise control for even greater automation.
Although the Sierra HD doesn’t feature a trick trailer-guidance system like the latest Super Duty, GM has improved the usability of all of its light- and heavy-duty trucks at low speeds via a new dealer-installed trailer-camera system ($999 for most setups) that includes add-on cameras to the exterior side mirrors, as well as a high-mounted unit that can look into the bed ($199 or $499 depending on the model) and another wireless camera that can be affixed to the back of a trailer ($349). The system integrates with the truck’s infotainment touchscreen, allowing for additional rearview perspectives beyond the available backup camera on the tailgate, automatic views of the blind-spot area when turning or changing lanes (like Honda’s LaneWatch), and assistance with hooking up a fifth-wheel or gooseneck trailer.
The plethora of truck and towing combinations make it difficult to gauge the 2017 Sierra HD’s overall prowess versus a similar Ford or Ram without driving them back-to-back. But the improvements gracing the latest GMCs make an already seriously capable pickup even more so—and without compromising it in a quest for maximum (albeit seldom-used) capabilities. While pricing for the 2017 models increases slightly over last year—2500HD Duramax versions start at $44,490—we still cringed at the $70,000 window stickers of the examples we drove. However, the same can be said for any modern, well-equipped heavy-duty pickup, and we can’t argue with the poise that the latest GMC Sierra HD exhibits while hauling a virtual fleet of Porsches.